Gas-liquid separator

ABSTRACT

A gas-liquid separator includes an inlet pipe and an inner pipe. The inlet pipe receives a swirling flow generating ribbon, and includes an exhaust port through which a separated gas flows out and a drain port through which a separated liquid flows out. The outer diameter of the inner pipe is smaller than the inner diameter of the inlet pipe. An end of the inner pipe is inserted into the exhaust port and is open at a location downstream of the swirling flow generating ribbon. A terminal end of the swirling flow generating ribbon includes a first terminal edge and a second terminal edge. The first and second terminal edges connect a first terminal end point, a second terminal end point, and a middle terminal end point.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-246468 filed on Dec. 17, 2015, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to a gas-liquid separator and more specifically to a gas-liquid separator that swirls a gas-liquid two-phase fluid flowing through a pipe by a swirling flow generating ribbon and guides liquid to an inner surface of the pipe by centrifugal force.

BACKGROUND ART

Conventionally, a gas-liquid separator that swirls a gas-liquid two-phase fluid flowing through a pipe by a swirling flow generating ribbon and guides liquid to an inner surface of the pipe by centrifugal force is known (see Patent Literature 1: JP 2003-62416A, for example). The swirling flow generating ribbon is formed from a helically twisted plate member. Further, a gas-liquid separator having a double pipe structure is also known (see Patent Literature 2: JP 2003-190725A and Patent Literature 3: JP 2005-160187A, for example). The double pipe structure includes a first pipe and a second pipe which has a larger diameter, and the downstream portion of the first pipe is inserted into the second pipe so that separated gas and liquid are separately discharged from respective pipes. In such gas-liquid separators, liquid (droplets) attached to the swirling flow generating ribbon flows toward the inner surface of the pipe while attached to the outer surface of the ribbon.

However, in the conventional gas-liquid separator, the terminal end of the swirling flow generating ribbon (the side end where the gas-liquid two-phase fluid flows out) includes a straight edge along the radial direction of the ribbon. Therefore, the liquid attached to portions of the swirling flow generating ribbon in the vicinity of the shaft center of the ribbon does not flow toward the inner surface of the pipe at the terminal end of the ribbon but re-scatters into the gas. As a result, the separation performance of the liquid deteriorates. Further, in the case of the double pipe structure where the downstream portion of the first pipe is inserted into the second pipe which has larger diameter, an installation space required for the gas-liquid separator is relatively large, which makes it difficult to install the gas-liquid separator in a limited space of an exhaust pipe of the internal combustion engine, for example.

SUMMARY OF THE INVENTION

Accordingly, the present disclosure is made considering the above issues and an object of the present disclosure is to provide a gas-liquid separator that can improve the separation performance of the liquid attached to the swirling flow generating ribbon and also can reduce a required installation space.

To achieve the above object, the present disclosure is a gas-liquid separator wherein a swirling flow generating ribbon formed from a helically twisted plate member swirls a gas-liquid two-phase fluid flowing through the pipe to guide a liquid toward an inner surface of the pipe by centrifugal force. The pipe includes an inlet pipe and an inner pipe. The inlet pipe receives the swirling flow generating ribbon. The inlet pipe includes, at a location downstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon, an exhaust port through which the gas flows out and a drain port through which the liquid flows out. The inner pipe is inserted into the exhaust port at an end. The inner pipe includes an outer diameter smaller than an inner diameter of the inlet pipe and an opening that is open at a location downstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon. The swirling flow generating ribbon includes, in a terminal end at a side where the gas-liquid two-phase fluid flows out, a first terminal end point that is set in an end of radially outward ends of the swirling flow generating ribbon, a second terminal end point that is set in another end of radially outward ends of the swirling flow generating ribbon, a middle terminal end point that is on an axial line of the swirling flow generating ribbon and set closer to a side where the gas-liquid two-phase fluid flows in than the first terminal end point and the second terminal end point, a first terminal edge connecting the first terminal end point and the middle terminal end point, and a second terminal edge connecting the second terminal end point and the middle terminal end point.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an entire system diagram illustrating an exhaust gas recirculation system of an internal combustion engine to which a gas-liquid separator according to the First Embodiment is applied.

FIG. 2 is a cross sectional view illustrating the gas-liquid separator according to the First Embodiment.

FIG. 3 is a perspective view illustrating a swirling flow generating ribbon according to the First Embodiment.

FIG. 4 is a side view illustrating the swirling flow generating ribbon according to the First Embodiment.

FIG. 5 is a cross sectional view along a line A-A shown in FIG. 3.

FIG. 6 is an overall explanatory diagram illustrating a flow of a gas-liquid two-phase fluid and flows of separated gas and liquid in the gas-liquid separator according to the First Embodiment.

FIG. 7 is an explanatory diagram illustrating a flow of the liquid attached to the swirling flow generating ribbon at a terminal end of the ribbon in the gas-liquid separator according to the First Embodiment.

FIG. 8 is a cross sectional view illustrating a gas-liquid separator according to the Second Embodiment.

FIG. 9 is an enlarged view of a portion B shown in FIG. 8.

FIG. 10 is a cross sectional view along a line C-C shown in FIG. 8.

FIG. 11 is an overall explanatory diagram illustrating the flow of the gas-liquid two-phase fluid and the flow of the separated gas and liquid in the gas-liquid separator according to the Second Embodiment.

FIG. 12 is an enlarged view illustrating the flow of the liquid in the gas-liquid separator according to the Second Embodiment.

FIG. 13 is an enlarged view of a portion B1 shown in FIG. 11.

FIG. 14A is a cross sectional view illustrating a first variation of the gas-liquid separator according to the First Embodiment.

FIG. 14B is a cross sectional view illustrating a second variation of the gas-liquid separator according to the First Embodiment.

FIG. 14C is a cross sectional view illustrating a third variation of the gas-liquid separator according to the First Embodiment.

FIG. 15A is a cross sectional view illustrating a primary section of a fourth variation of the gas-liquid separator according to the First Embodiment.

FIG. 15B is a cross sectional view illustrating a primary section of a fifth variation of the gas-liquid separator according to the First Embodiment.

FIG. 15C is a cross sectional view along a line D-D shown in FIG. 15B.

FIG. 16 is an enlarged cross sectional view illustrating a primary section of a first variation of the gas-liquid separator according to the Second Embodiment.

FIG. 17 is a cross sectional view illustrating a primary section of a second variation of the gas-liquid separator according to the Second Embodiment.

FIG. 18 is a cross sectional view illustrating a primary section of a third variation of the gas-liquid separator according to the Second Embodiment.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of a gas-liquid separator according to the present disclosure will be described in accordance with the First Embodiment and the Second Embodiment illustrated in the accompanying drawings.

First Embodiment

First, the configuration of a gas-liquid separator 20 in the First Embodiment will be separately described under headings “Overall Configuration of System”, “Detailed Configuration of Gas-Liquid Separator”, and “Detailed Configuration of Swirling Flow Generating Ribbon”.

(Overall Configuration of System) FIG. 1 is an entire system diagram illustrating an exhaust gas recirculation system of an internal combustion engine to which a gas-liquid separator according to the First Embodiment is applied.

Hereinafter, an overall configuration of the system in the First Embodiment will be described with reference to FIG. 1.

The gas-liquid separator 20 in the First Embodiment is applied to an exhaust gas recirculation system S of an internal combustion engine 1 shown in FIG. 1. Here, the internal combustion engine 1 shown in FIG. 1 is a diesel engine mounted in a vehicle as a driving source for traveling, and includes four cylinders (not shown). Each of the cylinders is connected to an intake passage 2 and an exhaust passage 3.

The intake passage 2 includes an intake port 2 a at an end. In order from a side where the intake port 2 a is disposed, an air cleaner 4 for filtering an intake air, a compressor 5 a of a turbocharger 5, and an intercooler 6 for cooling the intake air, and a throttle valve 7 for regulating an amount of the intake air are disposed. In order from a side where the internal combustion engine 1 is disposed, the exhaust passage 3 is provided with a turbine 5 b of the turbocharger 5, an exhaust purification catalyst 8 for purifying an exhaust gas, and an exhaust throttle valve 9 for regulating an amount of the exhaust gas. A muffler 10 is disposed downstream of the exhaust throttle valve 9, and an exhaust port 3 a is disposed downstream of the muffler 10.

The intake passage 2 is connected to the exhaust passage 3 via a low-pressure EGR passage 11 and a high-pressure EGR passage 12. Here, “EGR (Exhaust Gas Recirculation)” is a technology for taking out a part of the exhaust gas after combustion in the internal combustion engine 1 and for taking in the gas again. “EGR” is also referred to as exhaust gas recirculation.

The low-pressure EGR passage 11 connects a portion of the intake passage 2 located upstream of the compressor 5 a and a portion of the exhaust passage 3 located downstream of the exhaust purification catalyst 8. On the other hand, the high-pressure EGR passage 12 connects a portion of the intake passage 2 located downstream of the compressor 5 a and a portion of the exhaust passage 3 located upstream of the turbine 5 b. Thereby, the low-pressure EGR passage 11 returns the exhaust gas passing through the turbine 5 b to the intake air before the compressor 5 a. Further, the high-pressure EGR passage 12 returns the exhaust gas before flowing into the turbine 5 b to the intake air passing through the compressor 5 a.

The low-pressure EGR passage 11 is provided with an EGR cooler 13 for cooling the exhaust gas returning to the intake passage 2, and a low-pressure EGR valve 14 for regulating an amount of the exhaust air returning to the intake passage 2 via the low-pressure EGR passage 11. The high-pressure EGR passage 12 is provided with a high-pressure EGR valve 15 for regulating an amount of the exhaust air returning to the intake passage 2 via the high-pressure EGR passage 12.

The low-pressure EGR passage 11 can return the exhaust air without reducing an amount of the exhaust air passing through the turbine 5 b of the turbocharger 5 and can effectively reduce NOx. However, the cooling in the EGR cooler 13 brings an issue of concern to generate condensed water. When the condensed water flows downstream in the form of droplets each having a certain size, the droplets may collide with the rotor blades and the like of the compressor 5 a of the turbocharger 5 to give an impact to the rotor blades and the like. Therefore, in the First Embodiment, the gas-liquid separator 20 shown in FIG. 2 is provided downstream of the low-pressure EGR valve 14 and upstream of the compressor 5 a of the turbocharger 5 (i.e. at a location surrounded by a dashed line X in FIG. 1) to collect and drain the condensed water.

(Detailed Configuration of Gas-Liquid Separator) FIG. 2 is a cross sectional view illustrating the gas-liquid separator according to the First Embodiment. Hereinafter, the configuration of the gas-liquid separator 20 in the First Embodiment will be described in detail with reference to FIG. 2.

As shown in FIG. 2, the gas-liquid separator 20 in the First Embodiment includes an inlet pipe 21, an inner pipe 22, the drainpipe 23, a reservoir tank 24, a bypass pipe 25, and a swirling flow generating ribbon 30.

The inlet pipe 21 includes an end which is located upstream (right side in FIG. 2) in a flow direction of the gas-liquid two-phase fluid. This upstream end of inlet pipe 21 is in connection with the intake port 2 a and the low-pressure EGR valve 14. The inlet pipe 21 receives an exhaust in the mixture of a gas and particulate liquid (condensed water) (hereinafter, referred to as a gas-liquid two-phase fluid”). The swirling flow generating ribbon 30 is disposed within the inlet pipe 21 to swirl the flow of the gas-liquid two-phase fluid along an inner surface 21 c. Further, the inlet pipe 21 includes an exhaust port 21 a and a drain port 21 b at a downstream end (left side in FIG. 2) in the flow direction of the gas-liquid two-phase fluid. The swirling gas flows out through the exhaust port 21 a, and the liquid separated from the gas-liquid two-phase fluid flows out through the drain port 21 b. The exhaust port 21 a is open in an axial direction of the inlet pipe 21. The drain port 21 b is open in a radial direction of the inlet pipe 21 and downward in the direction of gravity. Note that “the direction of gravity” is a direction the gravity acts, and the downward direction in FIG. 2. Further, the inner surface 21 c of the inlet pipe 21 includes a tapered surface 21 d which gradually increases the inner diameter of the inlet pipe 21 in the flow direction of the gas-liquid two-phase fluid. The inlet pipe 21 has a first area 26A, a second area 26B, and a third area 26C. The first area 26A is an area upstream of the flow direction of the gas-liquid two-phase fluid from the tapered surface 21 d. The second area 26B is an area where the tapered surface 21 d is provided. The third area 26C is an area downstream of the flow direction of the gas-liquid two-phase fluid from the tapered surface 21 d. The inner diameter of the inlet pipe 21 is the smallest in the first area 26A and the gradually increases in the second area 26B. The inner diameter is the largest in the third area 26C. The swirling flow generating ribbon 30 is disposed in the first area 26A, and the exhaust port 21 a and the drain port 21 b are located in the third area 26C. Note that the liquid contained in the gas-liquid two-phase fluid flows into the drain port 21 b by centrifugal force (turning force) generated when the gas-liquid two-phase fluid is swirling. Accordingly, the drain port 21 b is open downward in the direction of gravity in the First Embodiment. However, the drain port 21 b is not limited to the above but may be open in any directions.

The inner pipe 22 is a straight pipe which has an outer diameter smaller than the inner diameter of the inlet pipe 21 at the third area 26C. An end 22 a of the inner pipe 22 is inserted into the exhaust port 21 a of the inlet pipe 21 so that the inner pipe 22 is disposed coaxially with the inlet pipe 21. The end 22 a includes an opening 22 b which is open at a location downstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon 30. Further, a downstream (left side in FIG. 2) end of the inner pipe 22 is in communication with the compressor 5 a of the turbocharger 5. The opening 22 b is open in an axial direction of the inner pipe 22. Specifically, the inlet pipe 21, the inner pipe 22, the exhaust port 21 a, and the opening 22 b are disposed coaxially with each other. In addition, the inner pipe 22 includes a vent hole 22 c which is disposed in a portion of the inner pipe 22 extending from the inlet pipe 21. The vent hole 22 c is open in a radial direction of the inlet pipe 21 and downward in the direction of gravity and is connected to a second end 25 b of the bypass pipe 25. Note that the vent hole 22 c may be open in other directions other than downward in the direction of gravity since the vent hole 22 c is an opening for generating a negative pressure in the reservoir tank 24 via the bypass pipe 25.

The exhaust port 21 a of the inlet pipe 21 is provided with a ring member 27 that fills a gap or clearance α between the inner surface 21 c and the inner pipe 22. The ring member 27 has a cylindrical shape which is configured to surround the entire circumference of the inner pipe 22. An outer surface of the ring member 27 contacts the inner surface 21 c of the inlet pipe 21 in an airtight state, and an inner surface of the ring member 27 contacts the outer surface of the inner pipe 22 in the airtight state. Further, the ring member 27 includes an inner end which faces inward of the inlet pipe 21. The axial position of an upstream end of the ring member 27 within the inlet pipe 21 is coincident with the axial position of the downward-most portion or edge of the drain port 21 b. In other words, the ring member 27 does not overlap an opening of the drain port 21 b but is disposed relative to the opening of the drain port 21 b not to form a gap in the axial direction between the upstream end of the ring member 27 and the opening of the drain port 21 b.

The drainpipe 23 is a T-shaped pipe and includes a first pipe member 23 a and a second pipe member 23 b. The second pipe member 23 b is perpendicular to the first pipe member 23 a and is connected to an axial center portion of the first pipe member 23 a to form the T-shaped pipe. The inlet pipe 21 extends through the first pipe member 23 a. A connection opening 23 c is formed at a connection between the first pipe member 23 a and the second pipe member 23 b. The connection opening 23 c faces the drain port 21 b. Thereby, the inlet pipe 21 is in communication with the second pipe member 23 b of the drainpipe 23 via the drain port 21 b and the connection opening 23 c. The liquid separated from the gas-liquid two-phase fluid within the inlet pipe 21 flows into the second pipe member 23 b via the drain port 21 b and the connection opening 23 c. Here, the inner diameter of the drain port 21 b has the substantially same size as the inner diameter of the connection opening 23 c of the drainpipe 23. The second pipe member 23 b includes a tapered diameter portion 23 d which extends downward in the direction of gravity relative to the axial direction of the inlet pipe 21, and the diameter of the tapered diameter portion 23 d gradually becomes smaller along the liquid flow direction. Accordingly, the inner diameter of a tip opening 23 e is smaller than the inner diameters of the connection opening 23 c and the drain port 21 b. Note that the first pipe member 23 a and the second pipe member 23 b are not limited to the cylindrical pipe but may be a square pipe (square pillar pipe) or the like. In addition, the second pipe member 23 b may not necessarily include the tapered diameter portion 23 d, and the inner diameter of the tip opening 23 e may not necessarily be smaller than the inner diameters of the connection opening 23 c and the drain port 21 b.

The reservoir tank 24 includes a tank body 24 a disposed below the second pipe member 23 b of the drainpipe 23. The tank body 24 a includes a connection opening 24 b formed at an upper portion thereof. The connection opening 24 b is connected to a tip portion 23 f of the second pipe member 23 b and is in communication with the tip opening 23 e. The liquid entered the second pipe member 23 b flows into the tank body 24 a via the tip opening 23 e and the connection opening 24 b to be retained in the tank body 24 a. Further, the tank body 24 a includes a vent hole 24 c formed on a side wall of a tank upper portion. The vent hole 24 c is connected to a first end 25 a of the bypass pipe 25. Note that the tank body 24 a includes a drain opening (not shown) which is formed at a tank bottom portion and is configured to open and close. The liquid may be discharged from the tank body 24 a via the drain opening when the liquid in the tank body 24 a reaches a predetermined amount. The position of the vent hole 24 c is not limited to the upper portion of the tank body 24 a, but the vent hole 24 c may be formed in any positions as long as air within the tank body 24 a can be suctioned.

The bypass pipe 25 is a pipe member both ends of which are open. The bypass pipe 25 includes a first end 25 a and a second end 25 b. The first end 25 a of the bypass pipe 25 is connected to the vent hole 24 c of the tank body 24 a, and the second end 25 b is connected to the vent hole 22 c of the inner pipe 22. Accordingly, the bypass pipe 25 communicates an upper space of the tank body 24 a with an inside of the inner pipe 22.

(Detailed Configuration of Swirling Flow Generating Ribbon) FIG. 3 is a perspective view illustrating the swirling flow generating ribbon according to the First Embodiment. FIG. 4 is a side view illustrating the swirling flow generating ribbon. FIG. 5 is a cross sectional view along a line A-A shown in FIG. 3. Hereinafter, the configuration of the swirling flow generating ribbon 30 according to the First Embodiment will be described in detail with reference to FIG. 3 to FIG. 5.

The swirling flow generating ribbon 30 is formed by helically twisting a plate member in a band shape. The swirling flow generating ribbon 30 is disposed in the first area 26A of the inlet pipe 21. A radial dimension R of the swirling flow generating ribbon 30 (see FIG. 4) is set to have the substantially same size as the inner diameter of the first area 26A. The swirling flow generating ribbon 30 is disposed coaxially with the inlet pipe 21, and a peripheral edge of the swirling flow generating ribbon 30 contacts the inner surface 21 c of the inlet pipe 21.

The swirling flow generating ribbon 30 includes a terminal end 31 which is located in a side where the gas-liquid two-phase fluid flows out. At the terminal end 31, the swirling flow generating ribbon 30 includes a first terminal end point 31 a, a second terminal end point 31 b, a middle terminal end point 31 c, a first terminal edge 32 a, and a second terminal edge 32 b. The first terminal end point 31 a is located in one of radially outside terminal ends of the swirling flow generating ribbon 30. The second terminal end point 31 b is located in the other of the radially outside terminal ends. The axial position of the first terminal end point 31 a is coincident with that of the second terminal end point 31 b. A terminal line L between the first terminal end point 31 a and the second terminal end point 31 b is perpendicular to an axial line O of the swirling flow generating ribbon 30. The middle terminal end point 31 c is located on the axial line O of the swirling flow generating ribbon 30, and is in a position closer to a side where the gas-liquid two-phase fluid flows in than the first terminal end point 31 a and the second terminal end point 31 b.

The first terminal edge 32 a of the swirling flow generating ribbon 30 connects the first terminal end point 31 a and the middle terminal end point 31 c. The second terminal edge 32 b connects the second terminal end point 31 b and the middle terminal end point 31 c. Specifically, in the terminal end 31 of the swirling flow generating ribbon 30, a V shaped space or area is defined by the first terminal edge 32 a, the second terminal edge 32 b, and the terminal line L.

Further, each of the first terminal edge 32 a and the second terminal edge 32 b of the swirling flow generating ribbon 30 includes a folding back structure 33. The folding back structure 33 is configured to be folded back toward the side where the gas-liquid two-phase fluid flows in. As shown in FIG. 5, the folding back structure 33 includes a first folding back piece 33 a and a second folding back piece 33 b. The first folding back piece 33 a is formed by folding back the tips of the first terminal edge 32 a and the second terminal edge 32 b toward a helical surface 30 a of the swirling flow generating ribbon 30. The second folding back piece 33 b is formed by folding back the tips of the first terminal edge 32 a and the second terminal edge 32 b toward the other helical surface 30 b. The folding back structure 33 is formed between the middle terminal end point 31 c and a position before the first terminal end point 31 a, and between the middle terminal end point 31 c and a position before the second terminal end point 31 b. Thereby, a gap or clearance β is formed between both radial ends of the folding back structure 33 and the inner surface 21 c of the inlet pipe 21 (see FIG. 2).

The swirling flow generating ribbon 30 is disposed in the first area 26A. However, at least the first terminal end point 31 a and the second terminal end point 31 b of the terminal end 31 are inserted into an area where the tapered surface 21 d is formed on the inner surface 21 c, that is the second area 26B.

The swirling flow generating ribbon 30 includes a starting portion 34 which is located in the side of the swirling flow generating ribbon 30 where the gas-liquid two-phase fluid flows in. At the starting portion 34, the swirling flow generating ribbon 30 includes a first starting point 34 a, a second starting point 34 b, and a middle starting point 34 c. The first starting point 34 a is located in one of radially outside starting ends of the swirling flow generating ribbon 30. The second starting point 34 b is located in the other of radially outside starting ends of the swirling flow generating ribbon 30. The middle starting point 34 c is located on the axial line O of the swirling flow generating ribbon 30. The axial position of middle starting point 34 c is coincident with the axial positions of the first starting point 34 a and the second starting point 34 b. Specifically, the middle starting point 34 c is set on the intersection of the axial line O and a starting line which connects the first starting point 34 a and the second starting point 34 b. The first starting point 34 a, the second starting point 34 b, and the middle starting point 34 c are aligned in the radial direction of the swirling flow generating ribbon 30. The starting portion 34 of the swirling flow generating ribbon 30 extends in the direction of gravity.

Now, the gas-liquid separation action of the gas-liquid separator 20 in the First Embodiment will be described. FIG. 6 is an overall explanatory diagram illustrating the flow of the gas-liquid two-phase fluid, and the flows of separated gas and liquid in the gas-liquid separator according to the First Embodiment. FIG. 7 is an explanatory diagram illustrating the flow of the liquid at the terminal end of the ribbon.

In the exhaust gas recirculation system S shown in FIG. 1, an outside air taken from the intake port 2 a and the exhaust gas taken from the exhaust passage 3 via the low-pressure EGR passage 11 flow into the compressor 5 a of the turbocharger 5 at a flow rate of 10 m/s to 100 m/s. At this time, moisture is contained in the outside air and the exhaust gas. These gases (the outside air and the exhaust gas) are cooled in the EGR cooler 13 so that the moisture is condensed into particulate liquid as condensed water, and the liquid is mixed with the gas such as air to form the gas-liquid two-phase fluid.

In the gas-liquid separator 20 of the First Embodiment, as shown in FIG. 6, the flow of the gas-liquid two-phase fluid turns into a swirling flow when the gas-liquid two-phase fluid in the inlet pipe 21 flows through the first area 26A along the swirling flow generating ribbon 30. Then, the centrifugal force is generated by the swirling flow, and the liquid having larger weight (mass) guided toward the inner surface 21 c of the inlet pipe 21 by the centrifugal force. The helical surfaces 30 a, 30 b of the swirling flow generating ribbon 30 are inclined relative to the flow direction of the gas-liquid two-phase fluid. Accordingly, the liquid contained in the gas-liquid two-phase fluid collides with the helical surfaces 30 a, 30 b and coheres, facilitating the formation of droplets.

Then, the liquid guided toward the inner surface 21 c coheres to become droplets and separated from the gas. The liquid separated from the gas flows from the second area 26B to the third area 26C by the swirling flow while the separated liquid is attached to the inner surface 21 c. The liquid reached the third area 26C flows downward through the drain port 21 b formed in the third area 26C by its own weight. Subsequently, the liquid flows into the second pipe member 23 b through the connection opening 23 c of the drainpipe 23, and flows along the second pipe member 23 b. Then, the liquid flows out of the second pipe member 23 b through the tip opening 23 e and flows into the tank body 24 a to be retained therein.

The liquid reached the third area 26C flows through the drain port 21 b by its own weight and downward toward the second pipe member 23 b since the drain port 21 b is open downward in the direction of gravity, and the second pipe member 23 b of the drainpipe 23 extends in the direction of gravity. Further, the outer diameter of the inner pipe 22 is smaller than the inner diameter of the inlet pipe 21 in the third area 26C so that the liquid attached to the inner surface 21 c of the inlet pipe 21 can be prevented from flowing into the inner pipe 22. Specifically, the liquid reached the third area 26C flows between the inlet pipe 21 and the inner pipe 22 so that the liquid can be prevented from flowing into the inner pipe 22. Moreover, the inner pipe 22 is inserted into the inlet pipe 21 so that it is not necessary to enlarge the diameter of the pipes and accordingly an installation space required for the gas-liquid separator 20 can be reduced.

Further, in the First Embodiment, the axial position of the upstream end of the ring member 27 relative to the inlet pipe 21 is coincident with the axial position of the downstream-most portion or edge of the drain port 21 b. Thereby, an axial gap is not created between the ring member 27 and the opening of the drain port 21 b. Therefore, even liquid reached the ring member 27 can smoothly flow out through the drain port 21 b.

Moreover, in the First Embodiment, the inner pipe 22 is in communication with the reservoir tank 24 via the bypass pipe 25. Accordingly, the gas flow through the inner pipe 22 generates a negative pressure in the reservoir tank 24 so that the liquid can smoothly flow through the drainpipe 23.

In addition, the gas flowing through the inlet pipe 21 flows into the inner pipe 22 from the opening 22 b open in the axial direction. At this time, the more the liquid moves downstream in the flow direction of the gas-liquid two-phase fluid, the more the liquid is separated from the gas. Subsequently, the gas flows to the compressor 5 a of the turbocharger 5 through the inner pipe 22. Here, the exhaust port 21 a of the inlet pipe 21 is provided with the ring member 27 that fills the clearance α between the inlet pipe 21 and the inner pipe 22. Therefore, the ring member 27 prevents the gas from leaking from the exhaust port 21 a of the inlet pipe 21 so that the gas separated from the gas-liquid two-phase fluid can smoothly flow into the inner pipe 22.

Further, the liquid is turned to droplets by contacting the helical surfaces 30 a, 30 b of the swirling flow generating ribbon 30. The liquid in the form of droplets flows radially outward of the swirling flow generating ribbon 30 by the swirling flow and is guided to the inner surface 21 c while attached to the helical surfaces 30 a, 30 b. At that time, the liquid in the form of droplets flows downstream of the flow direction of the gas-liquid two-phase fluid and also flows radially outward of the swirling flow generating ribbon 30.

At the terminal end 31 of the swirling flow generating ribbon 30, the liquid reached the first terminal edge 32 a or the second terminal edge 32 b while attached to the helical surfaces 30 a, 30 b flows radially outward of the swirling flow generating ribbon 30 along the first terminal edge 32 a or the second terminal edge 32 b and is guided toward the inner surface 21 c of the inlet pipe 21 as shown in FIG. 7 with arrows.

Specifically, in the first terminal edge 32 a, the first terminal end point 31 a which is set radially outward of the swirling flow generating ribbon 30 is located downstream of the flow direction of the gas-liquid two-phase fluid from the middle terminal end point 31 c which is located on the axial line O of the swirling flow generating ribbon 30. Also, in the second terminal edge 32 b, the second terminal end point 31 b which is set radially outward of the swirling flow generating ribbon 30 is located downstream of the flow direction of the gas-liquid two-phase fluid from the middle terminal end point 31 c which is located on the axial line O of the swirling flow generating ribbon 30. The liquid attached to the helical surfaces 30 a, 30 b of the swirling flow generating ribbon 30 flows downstream of the flow direction of the gas-liquid two-phase fluid and also flows radially outward of the swirling flow generating ribbon 30 by the swirling flow.

Therefore, the extending directions of the first terminal edge 32 a and the second terminal edge 32 b are substantially coincident with the flow directions (moving directions) of the liquid by the swirling flow while attached to the swirling flow generating ribbon 30. Thereby, in the terminal end 31 of the swirling flow generating ribbon 30, the liquid attached to the helical surfaces 30 a, 30 b is guided to the inner surface 21 c of the inlet pipe 21 while kept being attached to the first and second terminal edges 32 a, 32 b. Therefore, even the attached liquid in the vicinity of the axial line O of the swirling flow generating ribbon 30 can be prevented from re-scattering to the gas from the terminal end 31. In addition, it is possible to improve the separation performance of the liquid and to improve the collection rate of the liquid. Further, the flow of the gas is not inhibited and the gas flow resistance can be suppressed so as not to increase since there is no need to use a baffle, a filter or the like for separating the liquid.

Moreover, in the First Embodiment, each of the first terminal edge 32 a and the second terminal edge 32 b is provided with the folding back structure 33 which is folded back toward the side where the gas-liquid two-phase fluid flows in. The folding back structure 33 can prevent the liquid reached the first terminal edge 32 a or the second terminal edge 32 b while attached to the helical surfaces 30 a, 30 b from flowing downstream of the flow direction of the gas-liquid two-phase fluid. Specifically, the liquid flows radially outward of the swirling flow generating ribbon 30 through the gap or clearance between the first terminal edge 32 a and the first and second folding back pieces 33 a, 33 b, or the gap or clearance between the second terminal edge 32 b and the first and second folding back pieces 33 a, 33 b. Thereby, it is possible to prevent the liquid from being away from the first and second terminal edges 32 a, 32 b. Also, it is possible to guide the liquid to the inner surface 21 c of the inlet pipe 21 and to improve the separation performance of the liquid.

Further, in the First Embodiment, the folding back structure 33 includes the first folding back piece 33 a folded back toward the helical surface 30 a of the swirling flow generating ribbon 30, and the second folding back piece 33 b folded back toward the helical surface 30 b. Therefore, the liquid can be prevented from being away from the first and second terminal edges 32 a, 32 b even when the liquid is attached to the helical surface 30 a or the helical surfaces 30 b of the swirling flow generating ribbon 30.

In addition, the folding back structure 33 is formed between the middle terminal end point 31 c and the position before the first terminal end point 31 a, and also formed between the middle terminal end point 31 c and the position before the second terminal end point 31 b. Thereby, the gap β is formed between both radial ends of the folding back structure 33 and the inner surface 21 c of the inlet pipe 21. Therefore, the liquid prevented from flowing downstream of the flow direction of the gas-liquid two-phase fluid by the folding back structure 33 can flow downstream of the flow direction of the gas-liquid two-phase fluid at the radial ends of the folding back structure 33 through the gap 13. Thereby, it is possible to prevent the liquid from resided within the gap between the first terminal edge 32 a and the first and second folding back pieces 33 a, 33 b, and/or the gap between the second terminal edge 32 b and the first and second folding back pieces 33 a, 33 b. Also, it is possible to immediately guide the liquid to the inner surface 21 c of the inlet pipe 21.

In the First Embodiment, the inner surface 21 c of the inlet pipe 21 includes the second area 26B provided with the tapered surface 21 d which gradually increases the inner diameter of the inlet pipe 21 in the flow direction of the gas-liquid two-phase fluid. At least the first terminal end point 31 a and the second terminal end point 31 b of the terminal end 31 of the swirling flow generating ribbon 30 are inserted into the second area 26B provided with the tapered surface 21 d. Therefore, the liquid reached the first terminal end point 31 a or the second terminal end point 31 b along the first and second terminal edges 32 a, 32 b flows to the tapered surface 21 d. Thereby, the liquid guided to the inner surface 21 c along the first and second terminal edges 32 a, 32 b can smoothly flow to the drain port 21 b, which results in facilitating the guidance and separation of the liquid.

Now, effects will be described. According to the gas-liquid separator 20 in the First Embodiment, following effects can be obtained.

(1) A gas-liquid separator 20 for separating a liquid and a gas from gas-liquid two-phase fluid by centrifugal force, the gas-liquid separator 20 including:

a swirling flow generating ribbon 30 for swirling the gas-liquid two-phase fluid, the swirling flow generating ribbon formed from a helically twisted plate member and swirls the gas-liquid two-phase fluid;

an inlet pipe 21 that receives the swirling flow generating ribbon 30 and includes an inner surface 21 c to which a separated liquid is guided, the inlet pipe 21 including, at a location downstream of a flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon 30, an exhaust port 21 a through which the gas separated from the gas-liquid two-phase fluid flows out, and a drain port 21 b through which the liquid separated from the gas-liquid two-phase fluid flows out; and

an inner pipe 22 that is inserted into the exhaust port 21 a at an end, the inner pipe 22 including an outer diameter smaller than an inner diameter of the inlet pipe 21 and an opening 22 b that is open at a location downstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon 30,

wherein the swirling flow generating ribbon 30 includes, in a terminal end at a side where the gas-liquid two-phase fluid flows out,

the first terminal end point 31 a that is in an end (a first end) of radially outward ends of the swirling flow generating ribbon 30;

the second terminal end point 31 b that is in another end (a second end) of radially outward ends of the swirling flow generating ribbon 30;

the middle terminal end point 31 c that is on the axial line O of the swirling flow generating ribbon 30 and closer to a side where the gas-liquid two-phase fluid flows in than the first terminal end point 31 a and the second terminal end point 31 b;

the first terminal edge 32 a connecting the first terminal end point 31 a and the middle terminal end point 31 c, and

the second terminal edge 32 b connecting the second terminal end point 31 b and the middle terminal end point 31 c.

Thereby, the separation performance of the liquid attached to the swirling flow generating ribbon 30 can be improved and the installation space can be reduced.

(2) The swirling flow generating ribbon 30 includes the folding back structures 33 in the first terminal edge 32 a and the second terminal edge 32 b. Each of the folding back structures 33 is folded back toward the side where the gas-liquid two-phase fluid flows in. Thereby, in addition to the effect (1), the liquid can be guided to the inner surface 21 c of the inlet pipe 21 while prevented from being away from the first terminal edge 32 a or the second terminal edge 32 b. Also, the separation performance of the liquid can be further improved.

(3) The folding back structure 33 is formed between the middle terminal end point 31 c and a position before the first terminal end point 31 a, and between the middle terminal end point 31 c and a position before the second terminal end point 31 b. Thereby, in addition to the effect (2), the liquid can be guided to the inner surface 21 c of the inlet pipe 21 while prevented from residing within the gap between the first terminal edge 32 a and the first and second folding back pieces 33 a, 33 b, and/or the gap between the second terminal edge 32 b and the first and second folding back pieces 33 a, 33 b.

(4) The inner surface 21 c of the inlet pipe 21 includes the tapered surface 21 d which gradually increases the inner diameter of the inlet pipe 21 in the flow direction of the gas-liquid two-phase fluid. At least the first terminal end point 31 a and the second terminal end point 31 b of the swirling flow generating ribbon 30 are inserted into an area (the second area 26B) where the tapered surface 21 d is provided. Thereby, in addition to any one of the above effects (1) to (3), the liquid guided to the inner surface 21 c along the first and second terminal edges 32 a, 32 b can smoothly flow to the drain port 21 b, which facilitates the guidance and separation of the liquid.

(5) The inlet pipe 21 is provided with the drainpipe 23 connected to the drain port 21 b, and the reservoir tank 24 connected to the tip portion 23 f of the drainpipe 23. The inner pipe 22 is provided with the bypass pipe 25 in communication with an inside of the reservoir tank 24. Thereby, in addition to any one of the above effects (1) to (4), the gas flow through the inner pipe 22 can generate a negative pressure in the reservoir tank 24 so as to smooth the flow of the liquid through the drainpipe 23.

Second Embodiment

In a gas-liquid separator according to the Second Embodiment, an inlet pipe includes an upstream drain port and a pipe cooling structure or pipe cooler. An inner pipe includes a circular groove, a protrusion and a heater, and a swirling flow generating ribbon includes a ribbon cooling structure or ribbon cooler.

First, the configuration of a gas-liquid separator will be described. FIG. 8 is a cross sectional view illustrating a gas-liquid separator according to the Second Embodiment. Hereinafter, the configuration of a gas-liquid separator 40 according to the Second Embodiment will be described with reference to FIG. 8.

As shown in FIG. 8, the gas-liquid separator 40 according to the Second Embodiment includes an inlet pipe 41, an inner pipe 42, a first drainpipe 43, a reservoir tank 44, a second drainpipe 48, and a swirling flow generating ribbon 50.

The inlet pipe 41 is in communication with an intake port (not shown) and a low-pressure EGR valve (not shown) at an upstream end (right side in FIG. 8) thereof. The inlet pipe 41 includes the swirling flow generating ribbon 50 therewithin. An exhaust port 41 a and a first drain port 41 b are provided downstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon 50. A second drain port 41 e (an upstream drain port) is provided upstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon 50.

The exhaust port 41 a is an opening which is open in an axial direction of the inlet pipe 41 and through which the swirling gas flows out. The first drain port 41 b is an opening which is open in a radial direction of the inlet pipe 41 and downward in the direction of gravity, and through which the liquid separated from the gas-liquid two-phase fluid flows out. The second drain port 41 e is an opening which is open in a radial direction of the inlet pipe 41 and downward in the direction of gravity, and through which the liquid contained in the gas-liquid two-phase fluid before swirling.

The exhaust port 41 a receives an end 42 a of the inner pipe 42. A clearance α between the exhaust port 41 a and the inner pipe 42 is filled with a ring member 27 in an airtight state to prevent the gas-liquid two-phase fluid from leaking through the clearance α.

The inlet pipe 41 is in communication with the first drainpipe 43 via the first drain port 41 b. Also, the inlet pipe 41 is in communication with the second drainpipe 48 via the second drain port 41 e. The first drainpipe 43 is a T-shaped pipe and includes a first pipe member 43 a and a second pipe member 43 b. The second pipe member 43 b is perpendicular to the first pipe member 43 a and is connected to an axial center portion of the first pipe member 43 a to form the T-shaped pipe. The inlet pipe 41 extends through the first pipe member 43 a. A connection opening 43 c is formed at a connection part between the first pipe member 43 a and the second pipe member 43 b. The connection opening 43 c faces the drain port 41 b. Thereby, the inlet pipe 41 is in communication with the second pipe member 43 b of the first drainpipe 43 via the first drain port 41 b and the connection opening 43 c. Also, the second drainpipe 48 is a T-shaped pipe and includes a first pipe member 48 a and a second pipe member 48 b. The second pipe member 48 b is perpendicular to the first pipe member 48 a and is connected to an axial center portion of the first pipe member 48 a to form the T-shaped pipe. The inlet pipe 41 extends through the first pipe member 48 a. A connection opening 48 c is formed at a connection part between the first pipe member 48 a and the second pipe member 48 b. The connection opening 48 c faces the second drain port 41 e. Thereby, the inlet pipe 41 is in communication with the second pipe member 48 b of the second drainpipe 48 via the second drain port 41 e and the connection opening 48 c.

A tip portion 43 f of the second pipe member 43 b of the first drainpipe 43 is connected to a first connection opening 44 b formed in the reservoir tank 44. A tip portion 48 f of the second pipe member 48 b of the second drainpipe 48 is connected to a second connection opening 44 d formed in the reservoir tank 44. A tip opening 43 e formed in the tip portion 43 f of the second pipe member 43 b is in communication with the first connection opening 44 b. A tip opening 48 e formed in the tip portion 48 f of the second pipe member 48 b is in communication with the second connection opening 44 d.

Thereby, the liquid entered the first drainpipe 43 through the first drain port 41 b flows into a tank body 44 a of the reservoir tank 44 via the tip opening 43 e and the first connection opening 44 b to be retained in the tank body 44 a. Also, the liquid entered the second drainpipe 48 through the second drain port 41 e flows into the tank body 44 a via the tip opening 48 e and the second connection opening 44 d to be retained in the tank body 44 a.

Further, the inlet pipe 41 in the Second Embodiment includes a pipe cooling structure or pipe cooler 60 for cooling an inner surface 41 c of the inlet pipe 41. The pipe cooler 60 includes a cooling water circulation pipe 61, a first cooling water pipe 62, and a second cooling water pipe 63.

The cooling water circulation pipe 61 is a hollow cylindrical pipe having an inner diameter lager than the inlet pipe 41. The inlet pipe 41 has a double pipe structure in which the inlet pipe 41 extends through the cooling water circulation pipe 61 such that a part of the inlet pipe 41 is surrounded by the cooling water circulation pipe 61. Thereby, a pipe cooling water circulation space 61 a, which is a space surrounding the outer surface of the inlet pipe 41, is formed between the inlet pipe 41 and the cooling water circulation pipe 61. The cooling water circulation pipe 61 surrounds a part of the inlet pipe 41 in the axial direction between the first drain port 41 b and the second drain port 41 e, and the surrounded part includes an area in which the swirling flow generating ribbon 50 is disposed.

The first cooling water pipe 62 is a pipe through which cooling water (refrigerant) flows to the pipe cooling water circulation space 61 a. An end 62 a of the first cooling water pipe 62 is connected to a first opening 61 b formed in the cooling water circulation pipe 61, and the other end (not shown) is connected between an evaporator and an expansion valve of a refrigerating cycle of a vehicle air conditioner (not shown). The first opening 61 b is an opening which is radially opened in the pipe cooling water circulation space 61 a. Specifically, the first opening 61 b is formed by making a circular hole on the circumferential surface of the cooling water circulation pipe 61. As shown in FIG. 8, the first opening 61 b is at a location upstream in the flow direction of the gas-liquid two-phase fluid relative to the swirling flow generating ribbon 50 and is formed upward in the direction of gravity.

The second cooling water pipe 63 is a pipe through which the cooling water (refrigerant) from the pipe cooling water circulation space 61 a flows. An end 63 a of the second cooling water pipe 63 is connected to a second opening 61 c formed in the cooling water circulation pipe 61, and the other end (not shown) is connected between the compressor and the evaporator of the refrigerating cycle of the vehicle air conditioner (not shown). The second opening 61 c is radially open in the pipe cooling water circulation space 61 a. Specifically, the second opening 61 c is formed by making a circular hole on the circumferential surface of the cooling water circulation pipe 61. As shown in FIG. 8, the second opening 61 c is at a location downstream in the flow direction of the gas-liquid two-phase fluid relative to the swirling flow generating ribbon 50 and is formed downward in the direction of gravity.

Note that the locations of the first opening 61 b and the second opening 61 c are not limited to ones shown in FIG. 8 but the first opening 61 b and the second opening 61 c may be formed in any locations. For example, the first opening 61 b may be formed downstream in the flow direction of the gas-liquid two-phase fluid relative to the swirling flow generating ribbon 50, and the second opening 61 c may be formed upstream in the flow direction of the gas-liquid two-phase fluid relative to the swirling flow generating ribbon 50. Further, the opening directions of the first and second openings 61 b, 61 c are not necessarily in the direction of gravity since the cooling water circulates under the application of water pressure.

The inner pipe 42 is a straight pipe and an end 42 a of inner pipe 42 is inserted into the exhaust port 41 a of the inlet pipe 41. The end 42 a includes an opening 42 b which is open downstream of the flow direction of the gas-liquid two-phase fluid relative to the swirling flow generating ribbon 50 through which the gas separated from the liquid flows by the swirling flow.

An inner surface 42 d of the inner pipe 42 includes a plurality of circular grooves 42 e (two grooves in this embodiment). Each of the circular grooves 42 e is a circular recess formed in the inner pipe 42 and circumferentially extending along the inner pipe 42. In this embodiment, one of the two circular grooves 42 e is formed in a portion inserted into the inlet pipe 41, and the other circular groove 42 e is formed a porting extending from the inlet pipe 41. As shown in FIG. 9, each circular groove 42 e includes a first step surface 421 e, a second step surface 422 e, and a bottom surface 423 e.

The first step surface 421 e is a surface located upstream in the flow direction of the gas-liquid two-phase fluid among the surfaces defining the circular groove 42 e. The first step surface 421 e increases the inner diameter of the inner pipe 42 in a step-wise manner toward downstream in the flow direction of the gas-liquid two-phase fluid. Specifically, an inner diameter D2 of the inner pipe 42 defined within the circular groove 42 e is larger than an inner diameter D1 of the inner pipe 42 at a location upstream of the circular groove 42 e. In this embodiment, an angle θ₁ defined by the first step surface 421 e and an inner surface 421 d of the inner pipe 42 located upstream of the first step surface 421 e is set to 90° (degrees).

On the other hand, the second step surface 422 e is a surface located downstream in the flow direction of the gas-liquid two-phase fluid among the surfaces defining the circular groove 42 e. The second step surface 422 e decreases the inner diameter of the inner pipe 42 in the step-wise manner toward downstream in the flow direction of the gas-liquid two-phase fluid. Specifically, the inner diameter D2 of the inner pipe 42 defined within the circular groove 42 e is larger than an inner diameter D3 of the inner pipe 42 at a location downstream of the circular groove 42 e. In this embodiment, an angle θ₂ defined by the second step surface 422 e and an inner surface 442 d of the inner pipe 42 located downstream of the second step surface 422 e is set to 90° (degrees). Further, a height H2 of the second step surface 422 e has the same height as a height H1 of the first step surface 421 e.

The bottom surface 423 e is a bottom surface of the circular groove 42 e which circumferentially extends along the inner pipe 42 and is located between the first step surface 421 e and the second step surface 422 e.

An outer surface 42 f of the inner pipe 42 includes a protrusion 42 g formed in the portion inserted into the inlet pipe 41. Further, an electrical heating sheet (heater) 42 h is provided around a portion of the inner pipe 42 extending from the inlet pipe 41.

The protrusion 42 g radially extends from the outer surface 42 f and circumferentially extends along the inner pipe 42 to entirely surround the outer surface 42 f. The protrusion 42 g is formed above the first drain port 41 b of the inlet pipe 41 in the direction of gravity. A height H3 of the protrusion 42 g is set to be smaller than a height H4 of a clearance between the inner surface 41 c of the inlet pipe 41 and the outer surface 42 f of the inner pipe 42. Thereby, a gap or clearance is formed between a tip surface of the protrusion 42 g and the inner surface 41 c of the inlet pipe 41.

The electrical heating sheet 42 h is a flexible sheet including heating wires which generate heat by turning on a switch (not shown), and is wrapped around the inner pipe 42 to cover the outer surface 42 f. The outer surface 42 f of the inner pipe 42 is heated when the heating wires of the electrical heating sheet 42 h generates heat. In the Second Embodiment, one of the circular grooves 42 e is formed on the inner surface 42 d of the portion inserted into the inlet pipe 41, and the other of the circular grooves 42 e is formed on the inner surface 42 d of the portion extending from the inlet pipe 41. Accordingly, the electrical heating sheet 42 h heats a portion of the outer surface 42 f corresponding to the portion of the inner pipe 42 in which one of the circular grooves 42 e (the first step surface 421 e) is formed.

The basic configuration of the swirling flow generating ribbon 50 in the Second Embodiment is the same as that of the swirling flow generating ribbon 30 in the First Embodiment. Accordingly, a configuration of the Second Embodiment different from that of the First Embodiment will be described hereinafter.

In the Second Embodiment, the swirling flow generating ribbon 50 includes a ribbon cooling structure or ribbon cooler 70 for cooling a helical surface 50 a and another helical surface 50 b of the swirling flow generating ribbon 50. The ribbon cooler 70 includes a cooling water circulation space 71, a third cooling water pipe 72, and a fourth cooling water pipe 73.

As shown in FIG. 10, the plate member which forms the swirling flow generating ribbon 50 has a double structure which consists of a first plate member 50 c including the helical surface 50 a and a second plate member 50 d including the helical surface 50 b. The cooling water circulation space 71 is defined between the first plate member 50 c and the second plate member 50 d. Specifically, the cooling water circulation space 71 is formed inside of the swirling flow generating ribbon 50. The cooling water circulation space 71 is provided with a partition wall 71 c along the axial line O of the swirling flow generating ribbon 50. The partition wall 71 c divides the cooling water circulation space 71 into a first space 71 a and a second space 71 b. The first space 71 a and the second space 71 b are in communication with each other via a gap or clearance 71 d. The clearance 71 d is formed between the partition wall 71 c and a terminal end surface 51 d which closes a terminal end 51 of the swirling flow generating ribbon 50.

The third cooling water pipe 72 is a pipe through which cooling water flows to the cooling water circulation space 71. A first end 72 a of the third cooling water pipe 72 is connected to a third opening 54 e formed on a starting end surface 54 d which closes a starting end 54 of the swirling flow generating ribbon 50. A second end 72 b of the third cooling water pipe 72 radially extends through the inlet pipe 41 to communicate with the pipe cooling water circulation space 61 a. The third opening 54 e is formed by making a rectangular hole on the starting end surface 54 d and is open to the first space 71 a in the axial direction of the cooling water circulation space 71. The second end 72 b of the third cooling water pipe 72 extends through the inlet pipe 41 at a location where the second end 72 b faces the first opening 61 b of the cooling water circulation pipe 61.

The fourth cooling water pipe 73 is a pipe through which the cooling water discharged from the cooling water circulation space 71 flows. A first end 73 a of a fourth cooling water pipe 73 is connected to a fourth opening 54 f formed on the starting end surface 54 d which closes the starting end 54 of the swirling flow generating ribbon 50. A second end 73 b of the fourth cooling water pipe 73 radially extends through the inlet pipe 41 to communicate with the pipe cooling water circulation space 61 a. The fourth opening 54 f is formed by making a rectangular hole on the starting end surface 54 d and is open to the second space 71 b in the axial direction of the cooling water circulation space 71. The second end 73 b of the fourth cooling water pipe 73 extends through the inlet pipe 41 at a location downstream of the flow direction of the gas-liquid two-phase fluid from the first opening 61 b of the cooling water circulation pipe 61 and downward in the direction of gravity.

Now, the operation of a gas-liquid separator 40 in the Second Embodiment will be separately described under the headings “Liquid Collection Operation”, “Operation for Facilitating Coherence of Liquid” and “Operation for Facilitating Vaporization of Liquid”.

(Liquid Collection Operation) FIG. 11 is an overall explanatory diagram illustrating flows of the gas-liquid two-phase fluid, the separated gas and liquid in the gas-liquid separator according to the Second Embodiment. Hereinafter, an operation for collecting the liquid (liquid collection operation) according to the Second Embodiment will be described with reference to FIG. 11.

In the gas-liquid separator 40 of the Second Embodiment same as the First Embodiment, the gas-liquid two-phase fluid through the inlet pipe 41 swirls while flowing along the swirling flow generating ribbon 50 to generate centrifugal force so that the liquid is guided to the inner surface 41 c of the inlet pipe 41. The liquid guided to the inner surface 41 c coheres to become droplets and be separated from the gas. The gas separated from the liquid flows into the inner pipe 42 through the opening 42 b. On the other hand, the liquid separated from the gas flows into the first drainpipe 43 by its own weight through the first drain port 41 b of the inlet pipe 41, and flows through the first drainpipe 43 to the reservoir tank 44 to be retained therein.

Here, in the case where an amount of the liquid contained in the gas-liquid two-phase fluid is relatively larger, droplets having a certain size may be contained in the gas-liquid two-phase fluid without separating the liquid from the gas by swirling the gas-liquid two-phase fluid.

In the gas-liquid separator 40 of the Second Embodiment, the inlet pipe 41 includes, in addition to the first drain port 41 b, the second drain port 41 e at the location upstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon 50. Therefore, among the liquid contained in the gas-liquid two-phase fluid, liquid which is in the form of the droplets having a certain size before the gas-liquid two-phase fluid swirls and which flows downward in the direction of gravity by its own weight can flow out of the inlet pipe 41 through the second drain port 41 e by its own weight before reaching the swirling flow generating ribbon 50. The liquid flows through the second drainpipe 48, which is connected to the second drain port 41 e, toward the reservoir tank 44 to be retained in the reservoir tank 44.

As described above, in the gas-liquid separator 40 of the Second Embodiment, the second drain port 41 e is formed at a location upstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon 50. Accordingly, before the gas-liquid two-phase fluid swirls, it is possible to collect the liquid which can flow downward in the direction of gravity by its own weight without swirling the gas-liquid two-phase fluid among the liquid contained in the gas-liquid two-phase fluid. Therefore, it is possible to reduce an amount of the liquid contained in the gas-liquid two-phase fluid the gas-liquid two-phase fluid swirls so as to improve the liquid separation rate.

Further, in the gas-liquid separator 40 of the Second Embodiment, the liquid turned to droplets while guided to the inner surface 41 c of the inlet pipe 41 by the swirling flow flows to the third area 26C and then flows into the first drainpipe 43 through the first drain port 41 b by its own weight. The liquid flows through the first drainpipe 43 to the reservoir tank 44 to be retained in the reservoir tank 44. However, smaller droplets which cannot flow downward by their own weight may stay within the inlet pipe 41 while attached to the outer surface 42 f of the inner pipe 42.

On the other hand, a portion of the gas contained in the gas-liquid two-phase fluid does not flow into the inner pipe 42 but flows into a space between the inlet pipe 41 and the inner pipe 42. However, the flow of the gas between the inlet pipe 41 and the inner pipe 42 is blocked by the ring member 47. Accordingly, the swirling flow of the gas along the inner surface 41 c of the inlet pipe 41 collides with the ring member 47 and then flows backward along the outer surface 42 f of the inner pipe 42 toward the opening 42 b of the inner pipe 42.

Thereby, a portion of the droplets which cannot flow downward by its own weight but are attached to the outer surface 42 f of the inner pipe 42 may move toward the opening 42 b by the gas flowing to the opening 42 b of the inner pipe 42.

On the other hand, in the gas-liquid separator 40 of the Second Embodiment, the protrusion 42 g extending circumferentially is provided on the portion of the outer surface of the inner pipe 42 inserted into the inlet pipe 21 and at a location facing the first drain port 41 b.

Therefore, as shown in FIG. 12, the protrusion 42 g blocks the flow of droplets W which is forced to move toward the opening 42 b while attached to the outer surface 42 f of the inner pipe 42 by the gas flowing toward the opening 42 b along the outer surface 42 f of the inner pipe 42 after colliding with the ring member 47. The droplets W blocked by the protrusion 42 g gather each other. The gathered droplet flows downward by its own weight when its weight becomes larger enough and flows into the first drainpipe 43 through the first drain port 41 b.

Thereby, it is possible to prevent the droplets (liquid) from flowing into the inner pipe 42 and to appropriately collect the droplets even if the part of the droplets attached to the outer surface 42 f of the inner pipe 42 moves toward the opening 42 b of the inner pipe 42 with the gas. Therefore, it is possible to prevent the liquid in the form of the droplets from being mixed with the gas flowing through the inner pipe 42.

(Operation for Facilitating Coherence of Liquid) The flow of the gas-liquid two-phase fluid flowing through the inlet pipe 41 turns to the swirling flow when flowing along the swirling flow generating ribbon 50 at a certain flow rate. However, when the flow rate of the gas-liquid two-phase fluid is low, the flow rate of the swirling flow also becomes low, which weakens centrifugal force to be generated. In this case, it is difficult to guide the liquid to the inner surface 41 c of the inlet pipe 41 so that the coherence of the liquid is not facilitated and the liquid may not be separated from the gas as desired.

On the other hand, in the Second Embodiment, the gas-liquid separator 40 includes the pipe cooler 60, the inlet pipe 41 extends through the cooling water circulation pipe 61, and the pipe cooling water circulation space 61 a is formed between the inlet pipe 41 and the cooling water circulation pipe 61. In addition, the pipe cooling water circulation space 61 a is connected to the first and second cooling water pipes 62, 63 which are in turn connected to the refrigerating cycle of the vehicle air conditioner (not shown).

When the cooling water circulates in the refrigerating cycle, a part of the cooling water discharged from the expansion valve in the form of mist having low temperature and low pressure flows into the pipe cooling water circulation space 61 a through the first cooling water pipe 62. The cooling water entered the pipe cooling water circulation space 61 a flows in the axial direction of the inlet pipe 41, flows out of the pipe cooling water circulation space 61 a through the second opening 61 c, and returns to the refrigerating cycle via the second cooling water pipe 63.

The cooling water in the form of mist having low temperature and low pressure absorbs ambient heat and vaporizes while flowing through the pipe cooling water circulation space 61 a. Accordingly, the inlet pipe 41 and the cooling water circulation pipe 61 are cooled.

The gas-liquid two-phase fluid flows through the inlet pipe 41. When the gas-liquid two-phase fluid contacts the inner surface 41 c of the inlet pipe 41, the heat of the gas-liquid two-phase fluid is transferred to the inlet pipe 41 and absorbed so that the gas-liquid two-phase fluid is cooled. Accordingly, the temperature of the gas-liquid two-phase fluid is decreased so as to facilitate the liquid contained in the gas-liquid two-phase fluid to become droplets. Further, by facilitating the liquid to be droplets, the weight of each droplet becomes heavier so that the droplets (liquid) can be guided to the inner surface 41 c of the inlet pipe 41 even if the centrifugal force caused by the swirling flow is relatively weak. As a result, it is possible to improve the separation rate of the liquid from the gas-liquid two-phase fluid.

Further, the gas-liquid separator 40 of the Second Embodiment includes the ribbon cooler 70. Specifically, the swirling flow generating ribbon 50 disposed within the inlet pipe 41 has the double structure consisting of the first plate member 50 c and the second plate member 50 d, and the cooling water circulation space 71 is formed between the first plate member 50 c and the second plate member 50 d. Then, the cooling water circulation space 71 is in communication with the pipe cooling water circulation space 61 a via the third cooling water pipe 72 and the fourth cooling water pipe 73.

When the cooling water circulates in the refrigeration cycle of the vehicle air conditioner (not shown), a part of the cooling water flows into the pipe cooling water circulation space 61 a and then flows into the first space 71 a of the cooling water circulation space 71 via the third cooling water pipe 72. The cooling water entered the first space 71 a flows toward the terminal end 51 from the starting end 54 of the swirling flow generating ribbon 50, flows into the second space 71 b via the clearance 71 d to which the partition wall 71 c does not extend, and flows from the terminal end 51 to the starting end 54 within the second space 71 b. Then, the cooling water reached the starting end 54 is discharged to the pipe cooling water circulation space 61 a via the fourth opening 54 f formed on the starting end 54 and the fourth cooling water pipe 73.

In this embodiment, the second end 72 b of the third cooling water pipe 72 extends through the inlet pipe 41 at the location facing the first opening 61 b which is formed in the cooling water circulation pipe 61. The second end 73 b of the fourth cooling water pipe 73 extends through the inlet pipe 41 at the location downstream of the flow direction of the cooling water from the first opening 61 b. Accordingly, the cooling water from the pipe cooling water circulation space 61 a can flow from the first space 71 a to the second space 71 b.

The cooling water flown into the cooling water circulation space 71 absorbs the ambient heat and vaporizes while flowing through the cooling water circulation space 71 to cool the helical surfaces 50 a, 50 b which are surfaces of the swirling flow generating ribbon 50. Accordingly, when the gas-liquid two-phase fluid flowing through the inlet pipe 41 contacts the helical surfaces 50 a, 50 b of the swirling flow generating ribbon 50, the heat of the gas-liquid two-phase fluid is transferred to the swirling flow generating ribbon 50 so that the swirling flow generating ribbon 50 is cooled. Therefore, it is possible to facilitate the liquid contained in the gas-liquid two-phase fluid to turn into droplets and to improve the separation rate of the liquid from the gas-liquid two-phase fluid.

(Operation for Facilitating Vaporization of Liquid) In the gas-liquid separator 40 in the Second Embodiment, the gas-liquid two-phase fluid swirling, and the liquid is guided to the inner surface 41 c of the inlet pipe 41 to be separated from the gas and discharged via the first drain port 41 b. On the other hand, the gas separated from the liquid flows into the inner pipe 42 while keeping swirling and is supplied to the turbocharger 5 (not shown). However, if the liquid which is not separated from the gas exists, such non-separated liquid may flow into the inner pipe 42 with the gas.

In the case where the liquid flown into the inner pipe 42 with the gas has turned to droplets having certain weight, the liquid collides with rotor blades of the compressor 5 a of the turbocharger 5 and may give an impact thereto when the liquid flows downstream.

Accordingly, in the gas-liquid separator 40 of the Second Embodiment, the inner surface 42 d of the inner pipe 42 includes a plurality of (two in this embodiment) the circular grooves 42 e. Each of the circular grooves 42 e includes the first step surface 421 e, the second step surface 422 e, and the bottom surface 423 e.

The liquid flown into the inner pipe 42 is guided to the inner surface 42 d by the swirling gas flowing through the inner pipe 42 and coheres. The liquid flows into the circular grooves 42 e if the liquid in the form of droplets flows while attached to the inner surface 42 d.

At this time, as shown in FIG. 13, the gas flowing into the circular groove 42 e generates a turbulent flow within the circular groove 42 e and a negative pressure region H is generated along the first step surface 421 e upstream of the flow direction of the gas-liquid two-phase fluid. Accordingly, the droplets W flown into the circular grooves 42 e with the gas are pulled by the negative pressure region H to be drawn to the first step surface 421 e. Thereby, the droplets W stay within the circular groove 42 e, specifically in the vicinity of the first step surface 421 e.

The bottom surface 423 e of the circular groove 42 e extends in the circumferential direction of the inner pipe 42. Accordingly, the swirling gas circumferentially flows within the circular groove 42 e along the bottom surface 423 e. In addition, the droplets W staying within the circular groove 42 e also flows within the circular groove 42 e along the bottom surface 423 e together with the swirling gas. In other words, the gas and the droplets W swirl along the bottom surface 423 e within the circular groove 42 e. Then, the droplets W keep swirling along the bottom surface 423 e and evaporate.

It is possible to prevent the droplets W from flowing through the inner pipe 42 with the gas since the liquid (droplets W) flown into the inner pipe 42 swirls within the circular groove 42 e while pulled to the first step surface 421 e and evaporates.

Particularly, in the Second Embodiment, the inner surface 42 d of the inner pipe 42 is provided with a plurality of the circular grooves 42 e (two in this embodiment) so that there are a plurality of chances (twice in this embodiment) to keep the droplets W staying within the circular grooves 42 e and to evaporate the droplets W. Accordingly, more liquid can be vaporized so that the vaporization rate of the droplets can be improved.

Further, in the gas-liquid separator 40 in the Second Embodiment as shown in FIG. 11, the electrical heating sheet 42 h covers the outer surface 42 f of the portion of the inner pipe 42 extending from the inlet pipe 41. Therefore, the outer surface 42 f of the inner pipe 42 can be heated by the electrical heating sheet 42 h which is turned on to generate heat.

Thereby, it is possible to increase the temperature in the portion of the inner pipe 42 extending from the inlet pipe 41 and to facilitate the liquid flown into the inner pipe 42 with the gas to evaporate. As a result, it is possible to evaporate and vaporize the droplets flown into the inner pipe 42, to prevent the liquid in the form of the droplets from flowing downstream with the gas, and to improve the vaporization rate of the droplets.

In the Second Embodiment, the circular groove 42 e including the first step surface 421 e is formed on the portion of the inner surface 42 d of the inner pipe 42 extending from the inlet pipe 41 and is covered by the electrical heating sheet 42 h. Therefore, the portion of the outer surface 42 f of the inner pipe 42 provided with the circular groove 42 e can be heated by the electrical heating sheet 42 h.

Therefore, it is possible to facilitate the evaporation of the droplets staying in the vicinity of the first step surface 421 e of the circular groove 42 e and to effectively evaporate the droplets flown into the inner pipe 42.

Now, effects will be described. According to the gas-liquid separator 40 in the Second Embodiment, following effects can be obtained.

(6) The inlet pipe 41 includes the upstream drain port (the second drain port 41 e) through which the liquid flows out of the inlet pipe 41. The upstream drain port is provided at a location upstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon 50. Thereby, in addition to any one of the above effects (1) to (5), it is possible to collect the liquid which can flow downward by its own weight before the gas-liquid two-phase fluid swirls, and to improve the separation rate of the liquid.

(7) The inlet pipe 41 includes the pipe cooler 60 that cools at least a portion of the inlet pipe where the swirling flow generating ribbon 50 is disposed. Thereby, in addition to any one of the above effects (1) to (6), it is possible to decrease the temperature of the gas-liquid two-phase fluid flowing through the inlet pipe 41, to facilitate the coherence of the liquid and to improve the separation rate of the liquid.

(8) The swirling flow generating ribbon 50 includes the ribbon cooler 70 that cools surfaces of the ribbon (the helical surfaces 50 a, 50 b). Thereby, in addition to any one of the above effects (1) to (7), it is possible to decrease the temperature of the gas-liquid two-phase fluid flowing through the inlet pipe 41, to facilitate the coherence of the liquid and to improve the separation rate of the liquid.

(9) The inner surface 42 d of the inner pipe 42 includes the first step surface 421 e which increases the inner diameter of the inner pipe 42 downstream thereof. Thereby, in addition to any one of the above effects (1) to (8), it is possible to prevent the liquid in the form of the droplets from flowing downstream with the gas even if the droplets flow into the inner pipe 42.

(10) The inner surface 42 d of the inner pipe 42 includes the second step surface 422 e at the location downstream of the flow direction of the gas-liquid two-phase fluid from the first step surface 421 e. The second step surface 422 e decreases the inner diameter of the inner pipe 42 downstream thereof. Thereby, in addition to the effect (9), it is possible to prevent the liquid in the form of the droplets from flowing downstream from the vicinity of the first step surface 421 e and to suppress the liquid not to flow downstream as the droplets.

(11) The inner pipe 42 includes the protrusion 42 g on the outer surface 42 f of the portion the inner pipe inserted into the inlet pipe 41. The protrusion 42 g circumferentially extends along the outer surface 42 f. Thereby, in addition to any one of the above effects (1) to (10), it is possible to prevent the droplets which are not discharged from the inlet pipe 41 from being mixed with the gas flowing through the inner pipe 42.

(12) The inner pipe 42 includes a heater (the electrical heating sheet 42 h) that heats the portion the inner pipe extending from the inlet pipe 41. Thereby, in addition to any one of the above effects (1) to (11), it is possible to facilitate the vaporization of the liquid and to improve the vaporization rate of the droplets.

Although the gas-liquid separator of the present disclosure has been described based on the First Embodiment and the Second Embodiment, the specific configurations are not limited to these embodiments, and modifications and/or additions of the configurations may be made without departing from the gist of the invention recited in the claims.

In the First Embodiment, the folding back structures 33 are provided on the first terminal edge 32 a and the second terminal edge 32 b of the terminal end 31 of the swirling flow generating ribbon 30. However, the present disclosure is not limited to the above, but the folding back structures may not be formed as shown in FIG. 14A, for example. Even in this case, the extending directions of the first and second terminal edges 32 a, 32 b are substantially coincident with the flow direction of the liquid forced to flow by the swirling flow while attached to the swirling flow generating ribbon 30. Therefore, it is possible to guide the liquid while attached to the helical surfaces 30 a, 30 b to the inner surface 21 c of the inlet pipe 21 in the terminal end 31 of the swirling flow generating ribbon 30.

Further, in the First Embodiment, the tapered surface 21 d is formed on the inner surface 21 c of the inlet pipe 21, and the second area 26B provided with the tapered surface 21 d receives at least the first and second terminal end points 31 a, 31 b of the swirling flow generating ribbon 30. However, the tapered surface 21 d may not be formed as shown in FIG. 14B and FIG. 14C. Even in this case, the liquid separated from the gas-liquid two-phase fluid can flow into the drain port 21 b by the swirling flow.

In addition, as shown in FIG. 15A, the swirling flow generating ribbon 30 disposed in the first area 26A may extend such that the terminal end 31 is located in the third area 26C of the inlet pipe 21 in the vicinity of the opening 22 b of the inner pipe 22.

Moreover, as shown in FIG. 15B, the second area 26B provided with the tapered surface 21 d receives the first and second terminal end points 31 a, 31 b of the swirling flow generating ribbon 30, and both radial ends of the folding back structures 33 provided in the first and second terminal edges 32 a, 32 b of the swirling flow generating ribbon 30 may be extended along the inner surface 21 c of the inlet pipe 21. Specifically, each radial end of the folding back structures 33 may include an extension 35 which is inserted into the third area 26C of the inlet pipe 21. The extension 35 is formed to have a V-shape cross section defined by the first and second folding back pieces 33 a, 33 b (see FIG. 15C). By extending the extensions 35 such that the tips 35 a reach a location downstream from the opening 22 b of the inner pipe 22, the liquid flown between the first folding back piece 33 a and the second folding back piece 33 b of the folding back structure 33 can be guided to the inner surface 21 c without scattering in the inner pipe 22. In addition, the gaps β are maintained between the extensions 35 of the folding back structure 33 and the inner surface 21 c of the inlet pipe 21 so that the liquid flowing along the folding back structure 33 can be smoothly guided to the inner surface 21 c.

Further, in the First Embodiment, the starting portion 34 of the swirling flow generating ribbon 30 extends in the direction of gravity. However, the swirling flow generating ribbon 30 may be disposed such that the starting portion 34 horizontally extends relative to the direction of gravity, for example. In this case, it is possible for the liquid guided to the inner surface 21 c in the inlet pipe 21 to easily flow downward by its own weight and to effectively prevent the liquid separated from the gas from re-scattering.

Moreover, in the First Embodiment, the reservoir tank 24 is connected to the drainpipe 23 and retains the liquid separated from the gas-liquid two-phase fluid. However, the drainpipe 23 and/or the reservoir tank 24 may not be necessarily provided. The liquid separated in the inlet pipe 21 may not be retained but directly discharged through the drain port 21 b. Also, in the Second Embodiment, the second drainpipe 48 connected to the second drain port 41 e (the upstream drain port) may not be necessarily provided.

Further, in the First Embodiment, the first terminal edge 32 a and the second terminal edge 32 b are configured to extend straight to define the V-shaped space in the terminal end 31 of the swirling flow generating ribbon 30. However, the first terminal edge 32 a and the second terminal edge 32 b are not limited to the above. The first and second terminal edges 32 a, 32 b may be curved so that the terminal end 31 of the swirling flow generating ribbon 30 may have a U-shape as long as the middle terminal end point 31 c is located in the side where the gas-liquid two-phase fluid flows in relative to the first terminal end point 31 a and the second terminal end point 31 b.

In addition, the axial position of the first terminal end point 31 a is not necessarily coincident with that of the second terminal end point 31 b, but one of the first and second terminal end points 31 a, 31 b may be located closer to the side where the gas-liquid two-phase fluid flows in than the other of the first and second terminal end points 31 a, 31 b. In this case, the terminal line L may not be perpendicular to the axial line O of the swirling flow generating ribbon 30. Further, the middle terminal end point 31 c may be at a location radially deviated from the axial line O of the swirling flow generating ribbon 30 (at a location in the vicinity of the axial line O) as long as the middle terminal end point 31 c is located closer to the side where the gas-liquid two-phase fluid flows in than the first terminal end point 31 a and the second terminal end point 31 b. In other words, the shape of the swirling flow generating ribbon 30 is not limited to the one shown in the First Embodiment. The locations of the terminal end points and/or the starting end points, and/or the shapes of the terminal edges may be set as desired as long as the first and second terminal end points 31 a, 31 b respectively set in the terminal ends radially outward of the swirling flow generating ribbon 30, the middle terminal end point 31 c located closer to the side where the gas-liquid two-phase fluid flows in than the first and second terminal end points 31 a, 31 b, and the first and second terminal edges 32 a, 32 b connecting the first and second terminal end points 31 a, 31 b and the middle terminal end point 31 c are included.

In addition, the gas-liquid separator 40 of the Second Embodiment includes the pipe cooler 60 for cooling the inlet pipe 41, and the ribbon cooler 70 for cooling the swirling flow generating ribbon 50. However, the gas-liquid separator 40 is not limited to the above. It is possible to cool the gas-liquid two-phase fluid and to improve the coherence of the liquid contained in the gas-liquid two-phase fluid with one of the coolers 60, 70. Moreover, in the Second Embodiment, the pipe cooler 60 and the ribbon cooler 70 use the refrigerant of the vehicle air conditioner as the cooling water but may use an engine coolant (LLC: Long Life Coolant), for example.

Further, in the gas-liquid separator 40 of the Second Embodiment, the circular grooves 42 e are formed on the inner surface 42 d of the inner pipe 42, and each of the circular grooves 42 e includes the first step surface 421 e and the second step surface 422 e. However, as shown in FIG. 16, the inner surface 42 d of the inner pipe 42 may include only a first step surface 424 e which increases the inner diameter of the inner pipe downstream thereof. Also in this case, the negative pressure region can be generated along the first step surface 424 e so that the liquid in the form of the droplets can stay at a location in the vicinity of the first step surface 424 e and circumferentially swirl to evaporate.

Further, in the case only one first step surface is provided, a plurality of first step surfaces may be provided along the flow direction of the gas-liquid two-phase fluid. Specifically, the inner diameter of the inner pipe 42 may intermittently become larger at a plurality of locations where the first step surfaces are provided. In this case, it is possible to evaporate the droplets a plurality of times and to improve the vaporization rate of the droplets since the liquid may stay at the plurality of the locations in the vicinity of the first step surfaces to evaporate.

Further, in the Second Embodiment, the angle θ₁ is defined by the first step surface 421 e formed in the inner pipe 42 and the inner surface 421 d located upstream of the first step surface 421 e and the angle θ₁ is set to 90° (degrees). However, the angle θ₁ may be set to any angle as long as the angle can generate the negative pressure region H along the first step surface 421 e. Specifically, the angle θ₁ may be an acute angle set to be equal to or lower than 90° (degrees) as shown in FIG. 17.

Further, in the gas-liquid separator 40 of the Second Embodiment, the angle θ₂ is defined by the second step surface 422 e formed in the inner pipe 42 and the inner surface 422 d located downstream of the second step surface 422 e, and the angle θ₂ is set to 90° (degrees). However, the angle θ₂ may be set to any angle as long as the angle can prevent the droplets in the circular groove 42 e from moving downstream along the second step surface 422 e. Specifically, the angle θ₂ may be an acute angle set to be equal to or lower than 90° (degrees) as shown in FIG. 17.

Moreover, in the Second Embodiment, the axial positions of the circular grooves 42 e formed on the inner surface 42 d of the inner pipe 42 are not coincident with the axial position of the protrusion 42 g formed on the outer surface 42 f of the inner pipe 42. However, the axial positions are not limited to the above. For example, in the gas-liquid separator 40B shown in FIG. 18, the axial position of the circular groove 42 e may be coincident with the axial position of the protrusion 42 g by protruding a portion of the inner pipe 42 in which the inner surface 42 d is recessed. In this case, it is possible to form the circular groove 42 e and the protrusion 42 g at the same time and to suppress the reduction of the wall thickness of the inner pipe 42 due to the formation of the circular groove 42 e.

Further, in the Second Embodiment, the electrical heating sheet 42 h, which is flexible, is used as the heater or heating means for heating the outer surface 42 f of the inner pipe 42, but the heater is not limited to the above. For example, the inner pipe may be formed in a double pipe structure to circulate high temperature exhaust gas between the two pipe walls to heat the inner pipe as long as the portion of the inner pipe 42 extending from the inlet pipe 41 can be heated. In other words, the circulation structure for the exhaust gas may be used as a heater.

In addition, the gas-liquid separator 20 of the First Embodiment is disposed at the location downstream of the low-pressure EGR valve 14 and upstream of the compressor 5 a of the turbocharger 5 (i.e. at the location surrounded with a dashed line X in FIG. 1) in the exhaust gas recirculation system S. However, the location of the gas-liquid separator 20 is not limited to the above. The gas-liquid separator 20 may be disposed at a location where condensed water is produced in the exhaust gas recirculation system S. Accordingly, the gas-liquid separator 20 may be disposed at a location downstream of the intercooler 6 and upstream of the cylinder intake ports of the internal combustion engine 1 (i.e. at the location surrounded with a dashed line Y in FIG. 1).

Further, in the First Embodiment, the gas-liquid separator 20 is installed in a so-called transverse direction in which the flow direction of the gas-liquid two-phase fluid is horizontal with respect to the direction of gravity. However, the installation direction of the gas-liquid separator 20 in the present disclosure is not limited to the above, but may be appropriately selected considering factors such as a layout in the exhaust gas recirculation system S. Further, in the First Embodiment, the starting portion 34 extends in the direction of gravity. However, the extending direction of the starting portion 34 is not limited to the above but may be appropriately selected considering factors such as the layout of the gas-liquid separator 20 in the exhaust gas recirculation system S.

Moreover, in the First Embodiment, the internal combustion engine 1 is the diesel engine mounted in the vehicle. However, the internal combustion engine 1 is not limited to the diesel engine but may be a gasoline engine.

Further, in the First Embodiment and the Second Embodiment, the gas-liquid separators 20, 40 are applied to the exhaust gas recirculation system S of the internal combustion engine 1. However, the gas-liquid separators are not limited to the above but may be applied to a refrigeration cycle device, for example, to separate a gaseous refrigerant and a liquid refrigerant. In other words, the gas-liquid separator of the present disclosure can be applied to devices which separate the liquid and the gas from the gas-liquid two-phase fluid.

Moreover, the shape, the positions of the connection, and/or the diameter of each pipe (the inlet pipe, etc) are not limited to ones in the First Embodiment and the Second Embodiment but may be selected as desired. 

The invention claimed is:
 1. A gas-liquid separator for separating a liquid and a gas from gas-liquid two-phase fluid by centrifugal force, the gas-liquid separator comprising: a swirling flow generating ribbon for swirling the gas-liquid two-phase fluid, the swirling flow generating ribbon formed from a helically twisted plate member; an inlet pipe configured to receive the swirling flow generating ribbon, the inlet pipe comprising an inner surface to which a separated liquid is guided, and, at a location downstream of a flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon, an exhaust port through which the gas flows out and a drain port through which the liquid flows out; and an inner pipe inserted into the exhaust port at an end, the inner pipe comprising an outer diameter smaller than an inner diameter of the inlet pipe and an opening open at a location downstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon, wherein the swirling flow generating ribbon comprises, in a terminal end at a side where the gas-liquid two-phase fluid flows out: a first terminal end point in a first end of radially outward ends of the swirling flow generating ribbon; a second terminal end point in a second end of radially outward ends of the swirling flow generating ribbon; a middle terminal end point on an axial line of the swirling flow generating ribbon and at a location closer to a side where the gas-liquid two-phase fluid flows in than the first terminal end point and the second terminal end point; a first terminal edge connecting the first terminal end point and the middle terminal end point; and a second terminal edge connecting the second terminal end point and the middle terminal end point; and wherein the swirling flow generating ribbon comprises a folding back structure including a first folding back piece formed by folding back a first tip portion of the first terminal edge and a first tip portion of the second terminal edge toward a first helical surface of the swirling flow generating ribbon, and a second folding back piece formed by folding back a second tip portion of the first terminal edge and a second tip portion of the second terminal edge toward a second helical surface of the swirling flow generating ribbon.
 2. The gas-liquid separator according to claim 1, wherein the folding back structure is formed between the middle terminal end point and a position before the first terminal end point, and between the middle terminal end point and a position before the second terminal end point.
 3. The gas-liquid separator according to claim 1, wherein an inner surface of the inlet pipe comprises a tapered surface that gradually increases the inner diameter of the inlet pipe in the flow direction of the gas-liquid two-phase fluid, and wherein at least the first terminal end point and the second terminal end point of the swirling flow generating ribbon are inserted into an area where the tapered surface is provided.
 4. The gas-liquid separator according to claim 1, wherein the inlet pipe has a drainpipe connected to the drain port, and a reservoir tank connected to a tip portion of the drainpipe, and wherein the inner pipe has a bypass pipe in communication with an inside of the reservoir tank.
 5. The gas-liquid separator according to claim 1, wherein the inlet pipe comprises an upstream drain port through which a liquid flows out of the inlet pipe, the upstream drain port being at a location upstream of the flow direction of the gas-liquid two-phase fluid from the swirling flow generating ribbon.
 6. The gas-liquid separator according to claim 1, wherein the inlet pipe comprises a pipe cooler that cools at least a portion of the inlet pipe where the swirling flow generating ribbon is disposed.
 7. The gas-liquid separator according to claim 1, wherein the swirling flow generating ribbon comprises a ribbon cooler that cools a surface of the ribbon.
 8. The gas-liquid separator according to claim 1, wherein an inner surface of the inner pipe comprises a first step surface increasing the inner diameter of the inner pipe downstream thereof.
 9. The gas-liquid separator according to claim 8, wherein the inner surface of the inner pipe comprises a second step surface at a location downstream of the flow direction of the gas-liquid two-phase fluid from the first step surface, the second step surface decreasing the inner diameter of the inner pipe downstream thereof.
 10. The gas-liquid separator according to claim 1, wherein the inner pipe comprises a protrusion on an outer surface of a portion of the inner pipe inserted into the inlet pipe, the protrusion extending circumferentially along the outer surface.
 11. The gas-liquid separator according to claim 1, wherein the inner pipe comprises a heater configured to heat a portion the inner pipe extending from the inlet pipe. 